During a gas turbine engine starting, fuel is first provided to primary fuel nozzles which function as pilot nozzles, in order to deliver a very small amount of fuel near to the igniter system in the combustor for ignition at these nozzles to produce pilot torches in the combustor. Fuel is then provided to a set of main fuel nozzles, often through a manifold, to deliver the fuel at a relatively higher fuel pressure and high flow rate to start and maintain the continuous combustion in the combustor. The start flow needs to be accurately delivered and is normally metered by a metering valve/pump in demand fuel pumping systems. Controlling the start fuel flow with the metering valve/pump may lead to flow accuracy problems, given the factor that the fuel flow is in a very small amount in contrast to the maximum fuel flow to be pumped by the demand fuel pump, and that pump wear over the life of the pump could lead to problems with metering the start fuel flows. It is also desirable to eliminate the fuel metering valve/pump as a cost and weight savings.
Accordingly, there is a need to provide an improved low fuel flow metering control of a fuel system of gas turbine engines.